This invention relates to a direct-voltage flyback converter having a primary winding in series with the switching path of a controllable switch connected to a control device, a series circuit of a first capacitor and a first diode connected in parallel with the primary winding and a series circuit formed by a first coil, a second diode and the first capacitor being connected in parallel with the switching path.
To supply electronic devices, power supply devices are needed which supply one or several direct voltages. In the case of switched-mode direct-voltage converters, in particular, the basic types of flyback converter and forward converter must be distinguished. In this connection, a direct voltage obtained, for example, from the AC mains voltage by rectification and filtering is converted with the aid of a controllable switch into a rectangular voltage. This is transmitted with the aid of a transformer which, in the case of the flyback converter, also handles the energy storage. This is followed by rectification and filtering. During this process, a current only flows in the secondary circuit during the flyback phase in the case of a flyback converter.
The report "Kompakte Hochfrequenzoszilloskope erfordern eine effektive Stromversorgung" [compact high-frequency oscilloscopes require an effective power supply] in Elektronik Industrie 1, 1986, pages 44 to 48, by J. Vermolen and D. Mellis, describes how the efficiency in a switched-mode direct-voltage converter is improved by adding an unloading network in parallel with the input voltage. In FIG. 5 on page 46, an unloading network is shown in which a capacitor in series with a diode is being connected in parallel with a primary winding, and a coil in series with a further diode and the capacitor are connected in parallel with the switching path of the controllable switch. In this arrangement, the energy contained in the coil is fed back to the input voltage via the diode connected to the primary winding. In FIG. 7 on page 46, it is shown that the on-time of the controllable switch can be controlled in dependence on load fluctuations of the output voltage with the aid of a control device connected to the output voltage. However, such a control device activated from the secondary side is subject to additional power consumption.